TUMORS OF DOMESTIC ANIMALS 29 
tween which the epithelium sinks in, leaving an uneven surface not 
unlike the outside of a mulberry. At times the elevation of the 
core branches out, forming secondary plications, when the neoplasm 
assumes a grapelike or cauliflower formation. When the elevations 
are long and narrow the papilloma is known as villous papilloma. 
The weight of a downward-growing papilloma may stretch the core 
and form a pedunculated growth. 
Seats. — Papillomas occur in the shape of warts, grapelike or cauli- 
ilowerlike clumps, or as pedunculated growths, common in man and 
domestic animals. The skin about the head and neck and also the 
udders of cows and about the legs of horses are common places. 
Such superficially located papillomas are readily exposed to trauma- 
tism, which renders them susceptible to infections, resulting in ill- 
smelling discharges. Frequently papillomas are found on mucous 
surfaces including the lips, mouth, tongue, larynx, esophagus, stom- 
ach, intestines, kidney, bladder, and endometrium, and rarest of all 
on the choroid plexus in the cerebral ventricles. 
Structure. — On microscopic examination papillomas vary accord- 
ing to their shape, complexity of structure, and location. In the 
hard papilloma there is a connective-tissue stalk or core composed 
of fibrous-tissue bundles which are interlaced and contain a fair 
number of cells and a moderate amount of blood vessels. Strati- 
fied, squamous epithelium covers the stalk. The outermost cells are 
usually keratoid or horny. Papillomas growing on mucous mem- 
branes lined by columnar epithelium are softer on account of the 
more loosely arranged bundles, which are also fewer in number. 
The villous soft papillomas are found in the larynx, urinary blad- 
der, and mucous surface of the esophagus, as well as in the kidney, 
ovary, and uterus. Unlike other benign neoplasms, papillomas are 
not encapsulated, because of their outward growth from surfaces. 
Serous degeneration or dropsical conditions are frequently present 
in the polypoid type of papilloma. Mucous or myxomatous degen- 
eration is not infrequent in this type. Suppuration and ulceration 
are sometimes present. 
ADENOMA 
Definition. — Adenomas are usually benign epithelial neoplasms re- 
sembling the structure of a tubular or alveolar gland. They are usu- 
ally single, slow-growing neoplasms, differing in shape in their 
attempts to reproduce the many types of glands from which they 
have originated. 
Structure. — Adenomas, like their ancestors the glands, consist of 
epithelium, which corresponds to the parenchyma or functional part 
of the secreting gland, and the stroma forming the interstitial sup- 
porting tissue. 
As there are many varieties of glands, such as the sweat and 
sebaceous glands of the skin, the uterine, mammary, and salivary 
glands, the liver, renal, and seminal glands, so there may be many 
kinds of adenoma differing in the shape and size of the acini and 
in the character of the lining cells, which may be shorter or longer 
than those from which they originated. In the earlier stages adeno- 
mas resemble glandular hypertrophies so closely that it is difficult 
to distinguish them from each other. With the growth of the neo- 
plasm there is an increase in the complexity of structure resulting 
